despite the exit of combat troops, 50,000 troops remain there. they're turning it over to an iraqi military and government. what happens next? dan harris is in the palace. >> reporter: i'm outside one of saddam's old palace, which is part of an american military base, called camp victory. and beyond these walls there's about to take place what is called a change of command ceremony. the outgoing commander of u.s. forces in iraq, general ray odierno, is passing to general austin. as you mentioned, george, the remaining 50,000 troops here in iraq, the 50,000 american troops, are no longer technically combat troops. they are, instead, what is called advise and assist troops. they're job is to help the iraqi police and army stand up to take total control of security in this country. just a moment ago, we spoke with one of the top u.s. commanders on the ground here about what this day means. >> i think it's very significant. 7 1/2 years engaged here.